PRP injection The injection area was sterilized aseptically and 3-4 cc of PRP were percutaneously injected into the knee joints. The patients were asked to keep bending and stretching their injected knees several times so that the PRP could be evenly spread. If there was any intra-articular effusion identified, it was removed before the PRP injection. The patients were then advised to rest for 24 hours and not to move the affected knee in an aggressive manner.